Comment 15 for bug 1821594

I'm not sure how practical it will be to try and cleanup the leaked allocation in stable/pike because there was a pretty decent sized refactor of the allocation cleanup code in Queens:

https://review.openstack.org/#/c/498947/

Which would mean the backport to Pike would definitely not be clean. So I'll probably not put effort into backporting I29c5f491ec20a71283190a1599e7732541de736f to Pike but I can still fix the migration status getting stuck in 'confirming' issue with change Ic7d78ad43a2bad7f932c22c98944accbbed9e9e2.